For purposes of explanation, reference will be made to the use of the present invention with respect to the casting of motor cases (engine blocks). It should be understood by those of ordinary skill in the art that the invention is not limited to use in casting engine blocks and can be used in the casting of other products. Cylinder Blocks have traditionally been manufactured as a casting in Cast Iron. Recently Aluminium alloys have become the material of choice for cylinder blocks. While the weight and thermal conduction rates of aluminium have big advantages over cast iron, the actual casting of liquid aluminium is problematic. Conventional gravity pouring of aluminium alloys results in turbulent flow and the manifestation of oxides dispersed through the casting. These oxides often become the failure points for the casting in service. To overcome this problem with oxide formation, counter gravity filling of the liquid aluminium from the bottom of the mould has become the preferred method of casting. The major problem with counter gravity filling of moulds is the slow production rates, the mould filling system either low pressure or electromagnetic pump need to retain pressure until the casting has solidified, which for a cylinder block can be up to eight minutes. While the counter gravity filling is desirable, the solidification time and subsequent low productivity are not. To overcome this low productivity problem, methods of disconnecting the mould from the filling system and rotating the mould while the casting is still liquid have been developed. Once the mould and casting are rotated through 180° the risers which supply liquid metal during the solidification phase of the cast process are on top of the casting and gravity feed the required liquid metal into the contracting casting.
A major problem has been the differential pressures created in the liquid casting during rotation, which can result in casting imperfections; the present invention shows how to overcome this problem.